1. Technical Field
This invention is directed to the art of making and designing force-transmitting links, such as connecting rods, which operate to a large extent in compression and, more particularly, to a link which is effective to (i) connect at one end to a ceramic member while exhibiting a thermal expansion characteristic similar to such ceramic member and (ii) connect at the other end to a metal member while exhibiting a thermal expansion coefficient similar to such metal member.
2. Description of the Prior Art
With the advent of new research into engines having ceramic components effective to operate regularly at higher temperatures, for achieving lower fuel consumption and for operating with a greater variety of fuels, there has arisen a need for mechanical linkage which is both compatible with ceramic components to which it will be connected and with metal components to which it also will be connected at locations more remote from the engine. Connecting rods are one type of such linkage that can serve this purpose. In the newly designed engines, the piston and the cylinder may be comprised of ceramic. In this manner the engine can eliminate the necessity for a water cooling system and permit the combustion chamber elements to operate at very high temperatures. Frequently, such engines are referred to as adiabatic, that is, power is generated by such engines through pressure and volume changes substantially without heat loss. Although ceramic components can operate admirably in this environment, the economy and physical properties of metallic components at lower temperatures make metal a better choice for linkage members elsewhere or remote from the combustion area except, possibly, in critical wear zones.
Connecting rods heretofore have been made entirely of one material or, at best, have substituted another material for metal throughout the shank of the connecting rod while retaining metal only as a bearing surface at the openings of the connecting rod. Forged and/or cast iron connecting rods have proven the standard in production for water cooled gasoline engines for many years. The environmental temperature at the end of the rod which connects to the metallic piston in such applications, never exceeds about 250.degree. F. (see U.S Pat. No. 4,436,443). Iron connecting rods, made of powdered iron alloy, have been introduced recently as a manufacturing cost saver, but possess the same general expansion characteristics as the forged steel rods.
The difficulty that pervades all of the metal prior art connecting rod constructions is that the rod cannot be similar in thermal expansion characteristics to a ceramic piston or ceramic pin connecting to such piston. As a result, the metal rods give a hot clearance between the rod and ceramic pin which is excessive, with the result that the piston slaps the rod causing excessive wear and noise.
Considerable effort has been expended in designing connecting rods comprised substantially of reinforced plastics. In U.S. Pat. No. 4,458,555, the rod is made entirely of fiber-reinforced polymeric material. In U.S. Pat. Nos. 4,292,368; 4,038,885; 4,414,860; 4,425,820; 4,408,380; and 4,541,304, the disclosures employed fiber-reinforced plastic wound around metal sleeves for bearing surfaces or around a skeletal meal shank. In U.S. Pat. Nos. 4,350,056 and 4,391,161, bundles of silicon carbide reinforced plastic are cast-in-place with metal to form the connecting rod.
The major difficulty with fiber-reinforced plastic connecting rods, even if the plastic is used in a portin of the rod, is that such material prevents high temperature applications, such as to be experienced in a adiabtic diesel engine where the sustained temperatures at the connection of the rod to the pin will be about 500.degree. F.
It is an object of this invention to provide a compression linkage useful between swivel pins of differing materials and accompanying differing thermal expansion characteristics. It is more particularly an object of this invention to provide a compression linkage which permits connection to a pin operating at an elevated temperature of at least 500.degree. F. and connection to another pin operating in an environment substantially below said 500.degree. F., the linkage effectively translating compression loads therebetween without interfering with the free floating characteristics of the swivel pins; such operating conditions will be present in a two-stroke engine, but can be present in other engines in varying degree depending on the design.